1. Field of the Invention
The present device is directed generally to infrared (IR) optical systems. More specifically, the present invention is directed to IR optical systems with optical elements with plastic optically significant surface layers.
2. Background Information
Infrared electromagnetic radiation refers to the region of the electromagnetic spectrum between wavelengths of approximately 0.7 and 1000 xcexcm, which is between the upper limit of the visible radiation region and the lower limit of the microwave region. Infrared radiation is sometimes broken into three sub-regions: near-infrared radiation with wavelengths between 0.7-1 xcexcm, intermediate-infrared radiation with wavelengths between 1-20 xcexcm, and far-infrared radiation with wavelengths between 20-1000 xcexcm. The intermediate-infrared radiation region is often further broken into the short-wave (SWIR) region with wavelength limits of 1-3 xcexcm, mid-wave (MWIR) region with wavelength limits of 3-5 xcexcm, and the long-wave (LWIR) region with wavelength limits of 8-14 xcexcm.
Infrared radiation is produced principally by electromagnetic emissions from solid materials as a result of thermal excitation. The detection of the presence, distribution, and direction of infrared radiation requires techniques which are unique to this spectral region. The wavelengths of infrared radiation are such that optical methods may be used to collect, filter, and direct the infrared radiation. Photosensitive devices convert heat, or infrared electromagnetic radiation, into electrical energy and are often used as infrared sensitive elements. Such photosensitive devices respond in proportion to the number of infrared photons within a certain range of wavelengths to provide electrical energy.
An infrared optical element is transmissive to the wavelengths of radiation to be detected. Materials for the lenses are wavelength matched to the desired spectrum coverage. Although suitable materials may be selected based on the range of IR wavelengths, other material characteristics can impact the manufacturing of IR lenses. For example, the characteristics of silicon are advantageous for use as the material for IR lenses. Silicon can be cut into the desired lens geometry using a diamond point turning tool. However, the hardness of silicon results in slow material removal and wears the diamond tool faster than other IR materials like germanium. In extreme cases, the cost of manufacturing silicon into IR lenses can negate the cost savings from the bulk material. Therefore, a manufacturing process for IR lenses that is inexpensive and quick is desirable.
Exemplary embodiments of the present invention are directed to providing a laminated optical element with a polymer layer affixed to a substrate. The polymer layer has at least one optically significant surface.
In accordance with exemplary embodiments, a laminated optical element has a polymer layer disposed onto a first surface of a substrate made from a material that is essentially transparent in a desired IR range. The polymer layer is affixed with adhesive to the substrate and is formed into an optically significant surface. The polymer layer and the adhesive are each sufficiently thin to be at least 10%, preferably 30%, and most preferably 50% average normalized transmissive across the desired IR range. Alternatively, the polymer layer is bonded to the substrate or formed directly onto the substrate by molding or polymerization.
A method to adhere a polymer to a substrate is provided. Adhesive is applied to a first surface of a substrate and a polymer layer is compressively held to the first surface until the adhesive cures. Alternatively, the polymer layer is bonded to the first surface of a substrate by, for example, melting. The polymer layer is then manufactured with a desired prescription surface. Exemplary materials for the substrate are IR transmissive in a desired wavelength range and include silicon. Exemplary materials for the polymer layer are at least 30% IR transmissive when sufficiently thin and include fluoropolymers and polyethylene.